Radio signaling system



Jan. 4 1938. E. H. ARMSTRONG RADIO SIGNALING SYSTEM s sheets-sheet 1 Filed Sept. 14, 1935 SSL . INVENTOR. EdW/n H. Armsrronq.

ATTORNEYS.

Jan. 4, 1938. E. H. ARMSTRONG RADIO SIGNALING SYSTEM Filed sept. 14, 1935 5 Shee'ts-Sheet 2 NSM ' Jan. 4, 1938. E. H. ARMs'rRoNG RADIO SIGNALING SYSTEM 3 Sheetls-Sheet 5 Filed Sept. 14, 1935 Patented Jan. 4,1938

.aspro 'SIGNALING SYSTEM Y Edwin H. Armstrong, New York, N. Y. Application September .14, 1935, Serial No; 40,5047

` s claims. rc1. 25o- 2)` This invention has for its object the elimination of disturbances in radio signaling. It employs as its basic' principle the method shown yin my U. S. Patent 1,941,069 together withthe improvements described herein. The basic idea of that invention lies in introducing a characteristie into the transmitted wave which can not be produced by natural disturbances and proy viding a receiver which is insensitive to the type of current resulting from'the disturbances but fully responsive to a signal having the special characteristic.

The present inventionextends this principle by producing at the transmitter a type of wave which differs still more radically from the natural disturbances and by providing at the receiver a system which is still more insensitive to the natural disturbances but which is fully responsive to the new characteristics of the'transmitted wave.

Referring now to the figures which form a part of this specification, Fig. 1 illustrates the general arrangementof the transmitter and Fig. 2 illustrates the general arrangement of the receiver. Fig. 3 illustrates an alternative arrangement of the receiving apparatus.

Referring now to Fig. 1, I represents the master oscillator, 2 the phase shifter, 3 a correction system, 4 a frequency multiplying system, 5 the power amplifier and '6, 1 the ,radiator-all as described in the U. S. patent above referred to with the following exceptions. The phase shifter 2 and the correction system 3 instead of being designed to handle audible frequencies are designed for superaudible `frequencies of the order of 20,000 or more cycles depending on the wave vlength radiated by the transmitter.

8 represents a master oscillator of a second frequency modulation system, 9 the phase shifter, I the correction system for the signal input at II, l2, a frequency multiplying system, I3 a rectifier, I4 an oscillator for beating the output of the frequency multiplier I2 down to some super-audible intermediate value and I amplifier for supplying this current as a modulating current to the correction system 3 of the transmitter I-I.

The operation of the system of Fig. 1 may be understood from the following numerical example. Suppose that transmission is to be on 50,- 000.000 cycles and that the main system I--1 is designed to give a frequency deviation of 100,000 cycles plus and minus. This can be obtained by using the transmitting system described in my U. S. Patent No. 1,941,068. If the initial phase shifting operation is carried out at a frequency of 200,000 cycles and the frequency multiplication of l about 5,000 times is employed in the manner described in the patent, a frequency shift of this magnitude in its radiated wave is readily.

obtained. Suppose now a frequency of 1,000 cycles is to be transmitted. This current is supplied at point II thru the correction system I0 to the-phase shifter 9 of the auxiliary system. By means of the 4frequency multiplier I2 this phase shift may be multiplied several hundred or more times until a frequency deviation of, for example 10,000 cycles plus or minus is produced in the output of the lastl frequency multiplier. The actual mean frequency here may be of the order of 10,000,000 cycles which is deviating between 10,010,000 cycles and 9,990,000 cycles at a rate of 1,000 times per second. 'I'he heterodyne I4 is set, for example, at a frequency of 10,020,000 cycles. There is, therefore produced in the detector output La mean frequency of 20,000 cycles which varies between 10,000 cycles and 30,000 cycles at a rate of 1,000 times per second.

This becomes' the new modulating current for the main system and is supplied thru the correction system 3to the phase shifter 2. When there is no 1000 cycle modulation on at II' there will be produced in the antenna 6, 'I a frequency modulated current which varies between the limits 50,100,000 cycles and 49,900,000 cycles 20.- 000 times a second. When the 1,000 cycle current is supplied at the input II, then the deviation between the limits 50,100,000 cycles and 49,- 900,000 cycles, instead of occurring 20,000 times per second will occur at a variable rate between the limits of 10,000 and 30,000 times a second, and the change from 10.000 times to 30,000 times will in itself take place 1,000 times per second.

It will of course be understood that if the frequency of the current supplied at I I is changed (but the amplitude kept constant) that the number of times per second that the auxiliary and main frequency will change will correspond .to the frequency of modulation. A

Similarly if the amplitude of the modulating current at II is changed there will be a corresponding change in the extent of the frequency deviation of the output of the auxiliary system at I5 and there will be a corresponding change in the number of times that the 50,000,000 cycles deviate.

In this4 way there is produced an exceedingly complicated wave form which, however, follows 'faithfully the modulations impressed at il and which is totally unlike any wave form which can ,be produced by natural phenomena.

Referring now to Fig. 2 which illustrates the general method of reception 20, 2| represents the receiving antenna, 22 amplifier for the received frequency, 23 a rectifier and 24 an oscillator -for changing the incoming frequency to a lower intermediate frequency, 25 an amplifier for this frequency, 26 a second rectifier and 21 a second heterodyne for changing to a second intermediate frequency and 28 an amplifier for this frequency. 29 is a current limiter, 30 a filter for removing harmonics produced by thelimiter and 3l an amplifier for the output of the limiter. 32

is a selective system for translating the frequencyl deviations of greater extent into amplitude variations and 33 a rectifying system for converting these amplitude variations into a frequency modulated current having frequency deviations of the lesser extent. 34 is an amplifier for these currents, 35 a .current limiter, and 36 a filter for removing the harmonics produced by the limiter. 31 is an amplifier for the output of the current limiter 35. 38 is a selective system for translating the deviations of frequency of lesser amplitude into amplitude variations corresponding thereto and 39 a rectifier for converting the amplitude variations into currents which corresnond to the initial modulating current at the transmitter.

The manner of operation of this system may now be traced by assuming'the arrival of a wave having thecharacteristics already described in connection with the transmitter of Fig. 1. This wave is received by the antenna 20, 2| and amplied by the superheterodyne receiving system 22-28. The output of this amplifier which may be, for example, of the order of 400 kc., is sup. plied to the current limiter 29 and -amplitude variations removed. The output of the current limiter is then a constant amplitude current varying in frequency between 500,000 cycles and 300,000 cycles, 10,000 to 30,000 times a second, the change from the 10,000 time rate to the 30,000 time rate occurring 1,000 times per second. The second'harmonic produced in the current limiter 29 which is likely to be the most troublesome harmonic is the harmonic of the fundamental 400.000 cycle current and varies from 1,000,000 cycles to 600,000 cycles. It is eliminated by means of the filter 30.

The selective system 32 is designed on the principles explained in my U. S. Patent No. 1,941,- 069. Its method of operation is the same in the present arrangement as explained specifically in Patent No. 1,941,069 with vthis exception: That instead vof converting wide deviations of frequency which occur at an audible rate into amplitude variations of a corresponding audible rate it converts wide deviations of frequency which occur at a superaudible rate into amplitude variations corresponding to this superaudible rate. The rectifying system 33 converts these superaudible variations in amplitude into a. current of superaudible frequency; in this case one which varies between 10,000 and 30,000 cycles per second. This current is then amplified by the amplifier 34 and supplied to the current limiter 35 where amplitude variations are removed. 'I'he filter 36 is designed to remove frequencies down to 30,000 cycles. With the present selection of frequencies it is not possible to remove the second harmonic by a filter. It is therefore eliminated by means of a push-pull current limiter. The output of the current limiter is then amplified by the amplifier 34 and the frequency deviations between 10.000 and 30.000 cycles converted into amplitude variations by the selective system 38. 'I'his system may likewise be designed in accordance with the principles laid down in the patents already referred to. The modulations in amplitude, varying at a rate of 1,000 cycles-per second, are then converted by the rectifying system 39 into currents of 1,000 cycles frequency, corresponding to the initial modulatingvcurrent at the transmitter.

The operation of the receiving system in regard to the signaling current, while complex, may be definitely traced out and followed thruout its course thru the receiver. What happens under the influence of disturbing currents is much more diflicult to understand, since the phenomena are necessarily of a transient nature and vary greatly depending on the relative amplitude of the disturbance with respect to the signal and the type of the disturbance.

In general it may be observed that in order to produce a single cycle of current in the output of the receiver that a very involved series of frequency modulations must be produced before the current in the antenna may produce an effect at the receiver. Such an orderly arrangement of frequencies cannot be produced by any combination of the disorderly frequencies occurring in the natural disturbances. An insight into what occurs when a disturbance having the nature of a spectrum, such as the ordinary tube noise, is received simultaneously with the signal. Assuming that vthe disturbances are not greater than the amplitude of the signaling current, the effect of the first current limiter will be to do two things. It will eliminate all amplitude variations but will permit the disturbances to produce a cross modulation of the frequency of the signaling current. The effect of this will be to increase or decrease the frequency deviation which is occurring between (in the present example) 300 kc. and 500 kc. The result of this is merely to change the amplitude of the 10,000 to 30,000 cycle current which will be produced when the large deviations of the fundamental frequency are converted into amplitude variations and rectified. These variations in amplitude are of no importance since they lare removed by the second current limiter and only the variations of frequency of this current result in the ultimate output current in the receiver. It will be understood that in the first current limiting and converting operation that the effect described in my U. S. Patent No. 1,941,- 069 for reducing disturbancestakes place as described there except that the only frequencies of the disturbance spectrum which manifest themselves lie in a band 10,000 cycles to 30,000 cycles away on either side of the frequency of the signaling current. In addition, to this effect there is the additional effect which occurs at the second current limiter which is greatly enhanced by what may be called the polarization of the disturbing currents by the first current limiter into amplitude variations of the current supplied to the second current limiter. It will be understood of course that in the above discussion of what occurs during the simultaneous reception of signaling and disturbing currents that only the fundamental effects have been explained. There are numerous second order effects which occur but only those fundamental facts necessary to give an understanding of the principles involved have been considered.

Fig. 3 illustrates a modification of the arrangeto 40 of Fig. 2.

Referring now to the diagram 4I represents a band pass filter for passing the ontput of the rectifier 33 of Fig. 2. This would be of the order of 10,000 to 30,000 cycles for the specific example whichhas been given. 42 is an amplifier for this l current and 43 a balanced rectifier supplied with a heterodyning current from the oscillator 44 which is of considerably higher frequency than the output of the rectifier 33. 45 is a band pass filter designed to pass the combined frequency i either the sum or difference frequency) to the amplifier 46 and 41 is a 'current limiter. 48 is a second band pass filter which separates the signaling current. from any undesired harmonics which may be produced by the current limiter 4l. 49 is an amplifier, 50 a selective system for converting the variations in frequency into amplitude variations and 5i a balanced rectifylng system.

The operation of this modified form of receiver is as follows. The output of the first rectifying system. whose frequency is varying between 10,000 and 30,000 cycles per second is heterodyned up by beating it with a frequency which may be 45,000 cycles. This will produce in the output a frequency equal to the sum of the two which varies between 55,000 cycles and 75,000 cycles. This band of frequencies is passed by the filter 45 and the heterodyning frequency eliminated as well as other undesired frequencies. After amplification the 55,000 to 75,000 cycle current is passed thru the limiter and amplitude variations removed. The second harmonic which varies between 110,000 cycles and 150,000 cyeiess readily removed by the filter 48. After the removal of harmonics the output of the limiter is amplified, the frequency deviations are converted into amplitude variations by the selective system 50 and the amplitude variationsl converted into the currents corresponding to the original modulating current at vthe transmitterV by the balanced rectifying system 5I.

The above described system has the advantage over the arrangement of Fig. 2 that the second harmonic produced by the current limiter is definitely out of the signaling range and can be completely removed by filtering.

`1. The method of transmitting a radio signal which consists in producing a frequency modulated wave the frequency-of which is above audibility and the frequencyvariations of which correspond to the modulations of the signal to be transmitted, causing -said super-audible frequency-modulated wave to frequency-modulate a wave of still `higher frequency to an extent that the frequencydeviations of the second wave are greater in extent than the frequency deviation of the first wave and transmitting the second wave.

2. The methodwof receiving a radio signal 4 transmitted in accordance with the methodof claim 1, which'consists in removing amplitude variations from the received wave, passing the resultant current through a selective system to convert the wide variations of frequency of the transmitted wave into amplitude variations corresponding to the super-audible modulating frequency, rectifying these waves to produce a super-k audible frequency-modulated current varying in frequency at the rate of the signal, translating thevariations in frequency into variations in amplitude and rectifying the current to reproduce the original signal.

3. The method of receiving a radio signal transmitted in accordance with the method of claim 1, which consists in removing amplitude variations from the received wave, -passing the resultant current through a selective system to convert the wide variations of frequency of the transmitted wave into amplitude variations corresponding to the superaudible modulating frequency, rectifying these waves to produce a super-audible frequency-modulated current varying in frequency at the rate of the signal, eliminating amplitude fluctuations from this current, translating the variations in frequency into variations in amplitude and rectifying the current to reproduce the original signal.

4. The method of receiving a radio signal transmitted in accordance with the method of claim 1 which consists in removing amplitude variations from the received wave, translating the variations in frequency of the received wave into a current corresponding in frequency to the rate of these variations, eliminating amplitude variations from this current and translating the frequency variations therein into currents which correspond to the original signaling current at the transmitter.

5. The method of eliminating disturbances in radio signaling which consists in generating at the transmitter a frequency-modulatedwave containing the signal as a frequency modulation of a frequency-modulated wave, receiving such wave and subjecting the same to a compound frequency demodulation. p

6. A system for transmitting a radio signal comprising means for producing a frequency modulated wave the frequency of which is above audibility and the frequency variations of which correspond to the modulations of the signal to be transmitted, means for causing said super-audible frequency-modulated wave to frequency-modulate a wave of still higher frequency to an extent that the frequency deviations of the second wave are greater in extent than the frequency deviation ofthe first wave-and means for transmitting the second Wave.

'7. Ar system for receiving a radio signal transmitted in accordance with the system of claimI 6,

` which comprises means for removing amplitude variations from the received wave, means for translating the variations in frequency of the lreceived wave' into a current corresponding in frequency.v to the rate of these variations, means for eliminating amplitude variations from this curren't and means for translating the frequencyl variations therein into currents which correspond to the `original signaling current at the transmitter. 4 i

8. A system for eliminating disturbances in radio signaling, comprising means for generating 1 

